1. Field of the Invention
The invention relates to a dilute copper alloy material and a method of manufacturing a dilute copper alloy member excellent in characteristics of resistance to hydrogen embrittlement.
2. Description of the Related Art
In industrial products such as electronic devices and vehicles, a copper wire is sometimes used under a harsh condition. In order to provide a copper wire endurable under harsh condition, a dilute copper alloy material which can be manufactured by a continuous casting and rolling method, etc., and has an improved strength greater than that of pure copper while maintaining conductivity and elongation characteristics to a pure copper level has been being developed.
A dilute copper alloy material is demanded to be a soft conductor having a conductivity of not less than 98%, preferably not less than 102% as a general purpose soft copper wire or a soft copper material to which the softness is required. The intended purpose of such a soft conductor includes a cabling material for commercial solar cell, an enameled wire conductor for motor, a high-temperature application soft copper material used at from 200 to 700° C., a molten solder plating material not requiring annealing, a copper material excellent in thermal conductivity and a material alternative to high purity copper.
A raw material as the dilute copper alloy material is manufactured by basically using a technique of controlling oxygen in copper to not more than 10 mass ppm. It is expected to obtain a dilute copper alloy material having high productivity and excellent in conductivity, softening temperature and surface quality by adding a small amount of metal such as Ti into the base raw material so as to form a solid solution.
Regarding conventional softening, the result has been obtained in which the softening of a sample in which 4 to 28 mol ppm of Ti is added to electrolyte copper (not less than 99.996 mass %) occurs earlier than a sample without addition thereof (see, e.g., “Iron and Copper” by Hisashi Szuki and Mikihiro Sugano (1984), No. 15, 1977-1983). According to “Iron and Copper”, a decrease of sulfur incorporated into a solid solution due to formation of Ti sulfide causes softening to occur in early stage.
Meanwhile, it has been proposed to continuously cast in a continuous casting apparatus using a dilute alloy in which a small amount of Ti is added to oxygen-free copper (See JP patent Nos. 3050554, 2737954 and 2737965). Furthermore, a method of reducing oxygen concentration by a continuous casting and rolling method has been also proposed (See JP patent Nos. 3552043 and 3651386). In addition, it has been proposed that, when a copper material is manufactured directly from molten metal of copper by the continuous casting and rolling method, the softening temperature is lowered by adding a small amount of metal such as Ti, Zr or V (0.0007 to 0.005 mass %) to the molten metal of copper with an oxygen amount of not more than 0.005 mass % (see, e.g., JP-A-2006-274384). In this regard, however, the conductivity is not examined in JP-A-2006-274384 and the manufacturing conditions for achieving both of the conductivity and the softening temperature is unknown.
On the other hand, a method of manufacturing an oxygen-free copper material having a low softening temperature and high conductivity has been proposed. That is, a method has been proposed in which a copper material is manufactured by a drawing-up continuous casting apparatus using molten metal of copper in which a small amount of metal such as Ti, Zr or V (0.0007 to 0.005 mass %) is added to the oxygen-free copper with an oxygen amount of 0.0001 mass % (see, e.g., JP-A-2008-255417).
In general, a copper classified as oxygen-free copper (with an oxygen concentration of not more than 10 mass %) is used under a usage environment in which characteristics of resistance to hydrogen embrittlement are required. This is because, in case of using a cheap tough pitch copper in a hydrogen environment, steam generated by a reaction of cuprous oxide (Cu2O) in the tough pitch copper with hydrogen diffused into the copper occurs a hydrogen embrittlement phenomenon, which causes embrittlement of the material. By contrast, since oxygen-free copper includes a significantly small amount of oxygen, a copper oxide is hardly present in the copper. Accordingly, steam is not generated even if hydrogen is diffused into copper and embrittlement does not occur. Therefore, there is no choice but to use less than 2 mass ppm of oxygen-free copper in an environment with presence of hydrogen.